1. Field of the Invention
The present invention relates to a screw compressor having a lubricating oil system provided with a bearing part in which at least one temperature sensing element (temperature sensor) is arranged so that the temperature in the vicinity of the inner periphery surface of the bearing part can be directly measured and the detected temperature signal can be transferred outward of the casing of the compressor.
2. Background of the Invention
A screw compressor houses a male/female pair of screw rotors in the compressor; the rotor shaft is provided at each end (coupling side end or counter-coupling side end) regarding the male rotor or the female rotor; a radial bearing supports each rotor shaft. Further, a thrust bearing that receives the thrust force from each rotor is provided at the rotor shaft of the coupling side end or the counter coupling side end regarding each rotor. An example of this thrust bearing is a tilting pad bearing (a thrust bearing provided with tilting pads).
The rotor shaft at which the thrust bearing is arranged is provided with a thrust member 31 that is configured with a sleeve and a disc; thereby, the disc protrudes from the sleeve in the radial direction, and the inner periphery of the sleeve is fixed to the outer periphery of the rotor shaft, the inner periphery of the sleeve surrounding the outer periphery of the rotor shaft. On both the coupling side and the counter coupling side of the disc, a pads-retaining member is provided. The tilting pads are arranged on the coupling side and the counter coupling side of the disc, between the disc and the pads-retaining member on the coupling side as well as between the disc and the pads-retaining member on the counter coupling side; each tilting pad is fitted to the pads-retaining member on the coupling side or the counter coupling side so that the tilting pad can tilt against the radial direction as well as the hoop direction with regard to the rotor shaft on which the thrust member is fixed; each side of the disc of the thrust member slides on and comes in contact with the bearing surfaces of the tilting pads, while the thrust force is transferred to the thrust member (the disc) from the screw rotor.
In the screw compressor, since the rotors run at high speed, for instance, the radial bearing of a plain bearing type and the thrust bearing of a plain bearing type are used.
Heat is generated at the bearing surface (i.e. the radial bearing and the thrust bearing) of the bearing that supports the rotor; lube oil is usually supplied to the bearing surface so that a lube oil film is formed on the bearing surface and the generated heat is removed by the lube oil in the oil film. Thus, the temperature of each bearing is controlled so that the temperature does not exceed a certain level. Further, in a case where the lube oil film becomes out of order (e.g. oil film breakage) or the rotor comes in contact directly with the bearing surface, the bearing temperature abruptly increases and the components in the bearing are damaged. Hence, monitoring the bearing temperature is necessary so as to prevent the bearing temperature from reaching an abnormally high level.
In American Petroleum Institute Standard (API619/3rd edition) that includes rotary-type positive-displacement compressor, it is required that the temperature of the radial bearing and the thrust bearing in a screw compressor having a lubricating oil system be directly measured and controlled.
In a case where the radial bearing or the thrust bearing is of an oilless bearing type and the pressure level around the bearing is a level of the atmospheric pressure, it is not so difficult to arrange a temperature sensor at the bearing.
On the contrary, in a case where the bearing is of a lubricating oil system and the bearing is exposed to a high pressure equal to or higher than the discharging pressure level regarding the compressor, it is conventionally difficult to arrange a temperature sensor at the bearing. Hence, in conventional technologies, the temperature sensing part of the sensor is placed at the outer periphery surface of the bearing so as to measure the temperature thereof; then, the measured temperature is different from the temperature near to the oil film. Thus, it is unreasonable to say that the measured temperature is regarded as the true and accurate temperature of the bearing.
Even in a case where the sensing part of the temperature sensor is fitted to the bearing of the screw compressor having lubricating oil system, the measured temperature may be not accurate according to the fitting arrangement approaches of the sensor. Moreover, there are many problems to be solved in retrieving the temperature signals detected by the sensor from the outside of the compressor, or in maintaining the installed temperature-detecting element (or terminal). In addition, since the temperature level in the neighborhood of the bearing reaches 100° C. or higher, there may be another problem to be solved in retrieving the temperature signals detected by the sensor, or in providing durability regarding the lead-wire connected to the temperature-detecting element or terminal.
Patent Reference 1 (JP2006-112602) discloses a screw compressor provided with a resin layer that covers the bearing surface that supports the rotor shaft; thus, the temperature of the radial bearing or the thrust bearing can be measured. In the disclosed configuration, a hole (or a hole space with a bottom) is drilled on the bearing surface that supports the rotor shaft so that the hole space has an opening on the bearing surface as well as has a bottom in the bearing material; thus, the temperature sensing end-part of the sensor is inserted into and fixed in the hole space having the bottom; and, the gap space (or a clearance space) around the temperature sensing end-part of the sensor in the hole space is filled with a metal material for measuring temperature, the metal material being made from low melting white metal. Further, heat insulation material is provided so as to surround the filled metal material for measuring temperature.